Individual Beta-cells Research Articles

The Importance of Intra-Islet Communication in the Function and Plasticity of the Islets of Langerhans during Health and Diabetes.

Islets of Langerhans are anatomically dispersed within the pancreas and exhibit regulatory coordination between islets in response to nutritional and inflammatory stimuli. However, within individual islets, there is also multi-faceted coordination of function between individual beta-cells, and between beta-cells and other endocrine and vascular cell types. This is mediated partly through circulatory feedback of the major secreted hormones, insulin and glucagon, but also by autocrine and paracrine actions within the islet by a range of other secreted products, including somatostatin, urocortin 3, serotonin, glucagon-like peptide-1, acetylcholine, and ghrelin. Their availability can be modulated within the islet by pericyte-mediated regulation of microvascular blood flow. Within the islet, both endocrine progenitor cells and the ability of endocrine cells to trans-differentiate between phenotypes can alter endocrine cell mass to adapt to changed metabolic circumstances, regulated by the within-islet trophic environment. Optimal islet function is precariously balanced due to the high metabolic rate required by beta-cells to synthesize and secrete insulin, and they are susceptible to oxidative and endoplasmic reticular stress in the face of high metabolic demand. Resulting changes in paracrine dynamics within the islets can contribute to the emergence of Types 1, 2 and gestational diabetes.

1224-P: Glucagon Secretion Increases with Age in People with Type 2 Diabetes

It has been shown that the decline in the number of pancreatic beta cells and the insulin-secreting capacity of individual pancreatic beta cells progressively decreases with age, and this functional decline is accelerated by the addition of hyperglycemia. While, glucagon (GCG) is elevated in diabetes, and elevated GCG not only increases blood glucose levels (GLUs), but also decreases muscle mass due to protein metabolism leading to decrease in muscle glucose uptake, making blood glucose control more difficult. However, there are no reports yet regarding to age-related changes in GCG secretion. In this study, we analyze the age-related changes in GCG secretion in people with type 2 diabetes (T2D) after insulin treatment to remove glucose toxicity. A retrospective analysis was performed on people with T2D hospitalized for a period of 5 years from December 2017 in whom a test meal load (carbohydrate 75.5-70g, protein 8.5g, fat 28.5g) was performed before and after insulin treatment, and GLUs and GCG were measured. Insulin (IRI) and/or C-peptide (CPR) were also measured. A total of 121 patients (70 males, age 64.2 ± 11.6 years) were included in the analysis. After insulin treatment, GCG secretion was almost all lower than before treatment. GCG secretion increased with age (P=0.014). Insulinogenic Index decreased with age (R=-0.286 P=0.004), and IRI/GLU and CPR/GLU at 120 minutes after the test meal load also decreased with age (R=-0.314 P=0.001, R=-0.324 P=0.001). We confirmed that there is an increase in GCG secretion with aging in people with T2D. This might be one of the reasons for the decrease in muscle mass and physical activity in elderly people with T2D. Further studies are needed to expand the number including people with normal glucose and impaired glucose tolerance. Acknowledgments:The Cookie Testing Study Group provided support. Disclosure S.Kaneko: Advisory Panel; Lilly Diabetes, Speaker's Bureau; AstraZeneca, Novo Nordisk, Sumitomo Dainippon Pharma Co., Ltd., Mitsubishi Tanabe Pharma Corporation, Lilly Diabetes, Bayer Inc., Kowa Company, Ltd., Kyowa Kirin Co., Ltd. K.Motohashi: None. Y.Ueba: None. S.Tokumoto: None. Funding Cookie Testing Study Group

Exercise as a non-pharmacological intervention to protect pancreatic beta cells in individuals with type 1 and type 2 diabetes.

Diabetes is characterised by progressive loss of functional pancreatic beta cells. None of the therapeutic agents used to treat diabetes arrest this process; preventing beta cell loss remains a major unmet need. We have previously shown that serum from eight young healthy male participants who exercised for 8 weeks protected human islets and insulin-producing EndoC-βH1 cells from apoptosis induced by proinflammatory cytokines or the endoplasmic reticulum (ER) stressor thapsigargin. Whether this protective effect is influenced by sex, age, training modality, ancestry or diabetes is unknown. We enrolled 82 individuals, male or female, non-diabetic or diabetic, from different origins, in different supervised training protocols for 8-12 weeks (including training at home during the COVID-19 pandemic). EndoC-βH1 cells were treated with 'exercised' serum or with the exerkine clusterin to ascertain cytoprotection from ER stress. The exercise interventions were effective and improved [Formula: see text] values in both younger and older, non-obese and obese, non-diabetic and diabetic participants. Serum obtained after training conferred significant beta cell protection (28% to 35% protection after 4 and 8 weeks of training, respectively) from severe ER stress-induced apoptosis. Cytoprotection was not affected by the type of exercise training or participant age, sex, BMI or ancestry, and persisted for up to 2 months after the end of the training programme. Serum from exercised participants with type 1 or type 2 diabetes was similarly protective. Clusterin reproduced the beneficial effects of exercised sera. These data uncover the unexpected potential to preserve beta cell health by exercise training, opening a new avenue to prevent or slow diabetes progression through humoral muscle-beta cell crosstalk.

The role of GABA in islet function.

Gamma aminobutyric acid (GABA) is a non-proteinogenic amino acid and neurotransmitter that is produced in the islet at levels as high as in the brain. GABA is synthesized by the enzyme glutamic acid decarboxylase (GAD), of which the 65 kDa isoform (GAD65) is a major autoantigen in type 1 diabetes. Originally described to be released via synaptic-like microvesicles or from insulin secretory vesicles, beta cells are now understood to release substantial quantities of GABA directly from the cytosol via volume-regulated anion channels (VRAC). Once released, GABA influences the activity of multiple islet cell types through ionotropic GABAA receptors and metabotropic GABAB receptors. GABA also interfaces with cellular metabolism and ATP production via the GABA shunt pathway. Beta cells become depleted of GABA in type 1 diabetes (in remaining beta cells) and type 2 diabetes, suggesting that loss or reduction of islet GABA correlates with diabetes pathogenesis and may contribute to dysfunction of alpha, beta, and delta cells in diabetic individuals. While the function of GABA in the nervous system is well-understood, the description of the islet GABA system is clouded by differing reports describing multiple secretion pathways and effector functions. This review will discuss and attempt to unify the major experimental results from over 40 years of literature characterizing the role of GABA in the islet.

Effective Treatment of Diabetes Mellitus by Resonance Medicine.

The metabolic disorder known as diabetes mellitus (DM) has several different causes, distinguished by recurring hyperglycemia due to inadequate insulin secretion, insulin action, or both. T-lymphocytes target such cells for destruction, which include beta cells. Transplants of the pancreas, islets of Langerhans, and individual beta cells are all effective treatments for DM. Additionally, treating DM using stem cells is popular currently. The basis of stem cell therapy for DM is the replacement of beta cells, or dead pancreatic cells, with stem cells. After attaching to the tissues of the pancreas, the stem cells differentiate into active cells. An X-ray scanner is used to place a catheter into the pancreatic artery in DM, and the process lasts 90 minutes. The use of stem cells to replace dead pancreatic beta cells forms the cornerstone of stem cell treatment for DM. Transplants of the pancreas, islets of Langerhans, and individual beta cells are all effective treatments for insulin-dependent DM.In contrast to prior studies, where we only used low potencies of nosodes and organopreparations, our research used both high and low potencies of these substances. Choosing the strength of the nosode stomach cancer in the computer-connected device selector so that it will resonate with the nosode that is tested in the patient's device is the doctor's responsibility when using the bioresonance therapy method. The initial nosode, which is in the computer programme of the device for bioresonance therapy, is no longer tested when the stomach cancer nosode is tested in a patient along with the chosen potency of this nosode. The initial nosode in the bioresonance therapy device itself is still being studied in case the chosen nosode's potency is inadequate (the frequency of oscillations of the nosode is lower than the frequency of oscillations of the tumour).

The Role of Beta Cell Recovery in Type 2 Diabetes Remission.

Type 2 diabetes (T2D) has been considered a relentlessly worsening disease, due to the progressive deterioration of the pancreatic beta cell functional mass. Recent evidence indicates, however, that remission of T2D may occur in variable proportions of patients after specific treatments that are associated with recovery of beta cell function. Here we review the available information on the recovery of beta cells in (a) non-diabetic individuals previously exposed to metabolic stress; (b) T2D patients following low-calorie diets, pharmacological therapies or bariatric surgery; (c) human islets isolated from non-diabetic organ donors that recover from “lipo-glucotoxic” conditions; and (d) human islets isolated from T2D organ donors and exposed to specific treatments. The improvement of insulin secretion reported by these studies and the associated molecular traits unveil the possibility to promote T2D remission by directly targeting pancreatic beta cells.

Dual Mode of Action of Acetylcholine on Cytosolic Calcium Oscillations in Pancreatic Beta and Acinar Cells In Situ.

Cholinergic innervation in the pancreas controls both the release of digestive enzymes to support the intestinal digestion and absorption, as well as insulin release to promote nutrient use in the cells of the body. The effects of muscarinic receptor stimulation are described in detail for endocrine beta cells and exocrine acinar cells separately. Here we describe morphological and functional criteria to separate these two cell types in situ in tissue slices and simultaneously measure their response to ACh stimulation on cytosolic Ca2+ oscillations [Ca2+]c in stimulatory glucose conditions. Our results show that both cell types respond to glucose directly in the concentration range compatible with the glucose transporters they express. The physiological ACh concentration increases the frequency of glucose stimulated [Ca2+]c oscillations in both cell types and synchronizes [Ca2+]c oscillations in acinar cells. The supraphysiological ACh concentration further increases the oscillation frequency on the level of individual beta cells, inhibits the synchronization between these cells, and abolishes oscillatory activity in acinar cells. We discuss possible mechanisms leading to the observed phenomena.

Biphasic dynamics of beta cell mass in a mouse model of congenital hyperinsulinism: implications for type 2 diabetes.

Acute hyperglycaemia stimulates pancreatic beta cell proliferation in the mouse whereas chronic hyperglycaemia appears to be toxic. We hypothesise that this toxic effect is mediated by increased beta cell workload, unrelated to hyperglycaemia per se. To test this hypothesis, we developed a novel mouse model of cell-autonomous increased beta cell glycolytic flux caused by a conditional heterozygous beta cell-specific mutation that activates glucokinase (GCK), mimicking key aspects of the rare human genetic disease GCK-congenital hyperinsulinism. In the mutant mice, we observed random and fasting hypoglycaemia (random 4.5-5.4mmol/l and fasting 3.6mmol/l) that persisted for 15months. GCK activation led to increased beta cell proliferation as measured by Ki67 expression (2.7% vs 1.5%, mutant and wild-type (WT), respectively, p < 0.01) that resulted in a 62% increase in beta cell mass in young mice. However, by 8months of age, mutant mice developed impaired glucose tolerance, which was associated with decreased absolute beta cell mass from 2.9mg at 1.5months to 1.8mg at 8months of age, with preservation of individual beta cell function. Impaired glucose tolerance was further exacerbated by a high-fat/high-sucrose diet (AUC 1796 vs 966mmol/l × min, mutant and WT, respectively, p < 0.05). Activation of GCK was associated with an increased DNA damage response and an elevated expression of Chop, suggesting metabolic stress as a contributor to beta cell death. We propose that increased workload-driven biphasic beta cell dynamics contribute to decreased beta cell function observed in long-standing congenital hyperinsulinism and type 2 diabetes.

Multicolor Labeling and Tracing of Pancreatic Beta-Cell Proliferation in Zebrafish.

During embryogenesis, beta-cells arise from the dorsal and ventral bud originating in the endoderm germ layer. As the animal develops to adulthood, the beta-cell mass dramatically increases. The expansion of the beta-cell population is driven by cell division among the embryonic beta-cells and supplanted by neogenesis from post-embryonic progenitors. Here, we describe a protocol for multicolor clonal analysis in zebrafish to define the contribution of individual embryonic beta-cells to the increase in cell numbers. This technique provides insights into the proliferative history of individual beta-cells in an islet. This insight helps in defining the replicative heterogeneity among individual beta-cells during development. Additionally, the ability to discriminate individual cells based on unique color signatures helps quantify the volume occupied by beta-cells and define the contribution of cellular size to the beta-cell mass.

Determining Beta Cell Mass, Apoptosis, Proliferation, and Individual Beta Cell Size in Pancreatic Sections.

Pancreatic beta cells have a significant remodeling capacity which plays an essential role in the maintenance of glucose homeostasis. Beta cell apoptosis, replication, size, dedifferentiation, and (neo)generation contribute to the beta cell mass regulation. However, the extent of their respective contribution varies significantly depending on the specific condition, and it is the balance among them that determines the eventual change in beta cell mass. Thus, the study of the pancreatic beta cell mass regulation requires the determination of all these factors. In this chapter, we describe the quantification of beta cell replication based on the incorporation of thymidine analogs into replicated DNA strands and on the expression of Ki67 antigen and phosphorylation of histone H3. Beta cell apoptosis is analyzed by the TUNEL technique, and beta cell mass and cross-sectional area of individual beta cells are determined by computerized image processing methods.

Longevity of Beta Cells and Protein Complexes Revealed by Isotope Imaging

We discovered recently that long-lived cells (LLCs), such as neurons, contain long-lived proteins (LLPs) in the nucleus that can last a lifetime, and their decline during aging impairs nuclear function. Beta cells are LLCs with a slow cell replication process, yet it is unknown whether individual beta cells have different lifespans. We tested this hypothesis by using a hybrid microscopy and mapping platform (MIMS-EM) to identify beta cells and quantify cell and protein turnover in the islets of Langerhans. This is achieved by pulse-labelling mice with an 15N-rich diet followed by a chase period with a control 14N-rich diet for up to 2 years. Here, old cells and protein structures retain 15N while those that turnover incorporate 14N. The levels of 15N and 14N were measured with multi-isotope mass spectroscopy (MIMS) and the 15N-to-14N ratio reports on cell and protein turnover. Importantly, the MIMS data is correlated with scanning electron microscopy (EM) to create high-resolution maps of cells and intra-cellular structures overlaid with age information. Here we report the use of MIMS-EM on mouse islets to discover that beta cells have vastly different ages. In fact, while approximately 75% of beta cells replicate between 2-4 times, almost 25% of all beta cells does not replicate at all after weaning and remain quiescent for an entire lifetime, and therefore, are as old as cortical neurons. Such longevity was also found in other islet cell-types and at the protein super-complex level, where 15N accumulation on the primary cilium of beta cells strongly indicates that this important signaling structure is exceptionally long-lived. Strikingly, and similar to what is found in old rat neurons, beta cells from humans aged &amp;gt;60-years-old lose specific nuclear LLPs and show signs of impaired nuclear function. Together, our data shows that beta cell longevity is heterogeneous and identifies the loss of nuclear LLPs in human beta cells as a potential contributing factor to age-dependent loss of beta cell function. Disclosure R. Arrojo e Drigo: Stock/Shareholder; Self; VTV Therapeutics, Novo Nordisk A/S. B.H. Toyama: None. S. Tyagi: None. V. Lev-Ram: None. T.J.J. Deerinck: None. E.A. Bushong: None. R. Ramachandra: None. C. Lechene: None. M.H. Ellisman: None. M. Hetzer: None.

Investigation on the Protective Effect of Canagliflozin on Pancreatic Beta-Cell Mass Using SPECT/CT Imaging with 111In-Labeled Exendin-4

Background: Defects in insulin secretory function can be divided into two elements, the dysfunction of individual beta cells and a decrease of beta cell mass (BCM). Non-invasive methods to quantify BCM have not yet been established, and thus it is not possible to observe longitudinal changes in BCM. We developed [Lys12(111In-BnDTPA-Ahx)]exendin-4 ([111In]Ex4) as a radioactive probe targeting to the glucagon-like peptide-1 receptor with the aim of quantifying BCM by the measurement of probe accumulation in the pancreas. In this study, we investigated the protective effect of sodium-glucose co-transporter-2 (SGLT2) inhibitor on BCM using in-vivo SPECT/CT imaging with this probe. Aim: We tried to investigate longitudinal change in BCM of diabetic model mice administered with SGLT2 inhibitor using in-vivo SPECT/CT imaging with [111In]Ex4. Method: Male db/db mice were assigned into two groups: canagliflozin-administered group (group A) and non-administration group (group B). In-vivo SPECT/CT scans were performed before and after the intervention. The pancreatic uptake of [111In]Ex4 was evaluated using ROI with &amp;gt; 40% of the volume of the whole pancreas with the exception of the perirenal space. Result: The pancreatic uptake was significantly decreased in group B, on the other hand, no significant change was observed in group A. After the intervention, the pancreatic uptake was significantly higher in group A than group B. Discussion: SPECT/CT imaging analysis indicated that BCM was significantly larger in group A than group B after the intervention. It is considered that this difference was made by the protective effect of canagliflozin on BCM. Conclusion: It is considered that the protective effect of canagliflozin on BCM could be investigated using in-vivo SPECT/CT imaging with [111In]Ex4. Disclosure K. Hamamatsu: None. H. Fujimoto: None. N. Fujita: None. T. Murakami: None. M. Shiotani: Employee; Self; Mitsubishi Tanabe Pharma Corporation. H. Saji: Research Support; Self; Nihon Medi-Physics Co.,Ltd. N. Inagaki: Research Support; Self; Daiichi Sankyo Company, Limited, AstraZeneca, Ono Pharmaceutical Co., Ltd., Sanofi K.K., Mitsubishi Tanabe Pharma Corporation, Takeda Pharmaceutical Company Limited, Japan Tobacco Inc., MSD K.K., Sumitomo Dainippon Pharma Co., Ltd., Nippon Boehringer Ingelheim Co. Ltd., Novartis Pharma K.K., Kissei Pharmaceutical Co., Ltd., Novo Nordisk Pharma Ltd., Eli Lilly and Company, Sanwa Chemical Industrial Co., Ltd., Teijin Pharma Limited.

Impaired beta cell sensitivity to incretins in type 2 diabetes is insufficiently compensated by higher incretin response

Background and aimsThe incretin effect is impaired in type 2 diabetes (T2D), but the underlying mechanisms are only partially understood. We investigated the relationships between the time course of the incretin effect and that of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) during oral glucose tolerance tests (OGTTs), thereby estimating incretin sensitivity of the beta cell, and its associated factors. Methods and resultsEight patients with T2D and eight matched subjects with normal glucose tolerance (NGT) received 25, 75, and 125 g OGTTs and corresponding isoglycemic glucose infusions (IIGI). The time course of the incretin effect, representing potentiation of insulin secretion by incretins (PINCR), was determined by mathematical modelling as the time-dependent fold increase in insulin secretion during OGTT compared to IIGI. The time course of PINCR was correlated with that of both GIP and GLP-1 in each subject (median r = 0.67 in NGT and 0.45 in T2D). We calculated an individual beta cell sensitivity to incretins (SINCR) using a weighted average of GIP and GLP-1 (pooled incretin concentration, PIC), as the slope of the relationship between PINCR and PIC. SINCR was reduced in T2D (p < 0.01). In the whole group, mean PIC, GIP and GLP-1 concentrations during the OGTT were inversely correlated with SINCR, but T2D had lower PIC, GIP and GLP-1 levels at the same SINCR (p < 0.05). ConclusionRelative incretin insensitivity is partly compensated for by higher incretin secretory responses. However, T2D shows both impairment in incretin sensitivity and abnormal compensation by incretin secretion.

Conditional islet hypovascularisation does not preclude beta cell expansion during pregnancy in mice.

Endothelial-endocrine cell interactions and vascular endothelial growth factor (VEGF)-A signalling are deemed essential for maternal islet vascularisation, glucose control and beta cell expansion during mouse pregnancy. The aim of this study was to assess whether pregnancy-associated beta cell expansion was affected under conditions of islet hypovascularisation. Soluble fms-like tyrosine kinase 1 (sFLT1), a VEGF-A decoy receptor, was conditionally overexpressed in maternal mouse beta cells from 1.5 to 14.5days post coitum. Islet vascularisation, glycaemic control, beta cell proliferation, individual beta cell size and total beta cell volume were assessed in both pregnant mice and non-pregnant littermates. Conditional overexpression of sFLT1 in beta cells resulted in islet hypovascularisation and glucose intolerance in both pregnant and non-pregnant mice. In contrast to non-pregnant littermates, glucose intolerance in pregnant mice was transient. sFLT1 overexpression did not affect pregnancy-associated changes in beta cell proliferation, individual beta cell size or total beta cell volume. Reduced intra-islet VEGF-A signalling results in maternal islet hypovascularisation and impaired glycaemic control but does not preclude beta cell expansion during mouse pregnancy.

Heterogeneity of the Pancreatic Beta Cell.

The pancreatic beta cell functions as a key regulator of blood glucose levels by integrating a variety of signals in response to changing metabolic demands. Variations in beta cell identity that translate into functionally different subpopulations represent an interesting mechanism to allow beta cells to efficiently respond to diverse physiological and pathophysiological conditions. Recently, there is emerging evidence that morphological and functional differences between beta cells exist. Furthermore, the ability of novel single cell technologies to characterize the molecular identity of individual beta cells has created a new era in the beta cell field. These studies are providing important novel information about the origin of beta cell heterogeneity, the type and proportions of the different beta cell subpopulations, as well as their intrinsic properties. Furthermore, characterization of different beta cell subpopulations that could variably offer protection from or drive progression of diabetes has important clinical implications in diabetes prevention, beta cell regeneration and stem cell treatments. In this review, we will assess the evidence that supports the existence of heterogeneous populations of beta cells and the factors that could influence their formation. We will also address novel studies using islet single cell analysis that have provided important information toward understanding beta cell heterogeneity and discuss the caveats that may be associated with these new technologies.

Inter-organ communication and regulation of beta cell function.

The physiologically predominant signal for pancreatic beta cells to secrete insulin is glucose. While circulating glucose levels and beta cell glucose metabolism regulate the amount of released insulin, additional signals emanating from other tissues and from neighbouring islet endocrine cells modulate beta cell function. To this end, each individual beta cell can be viewed as a sensor of a multitude of stimuli that are integrated to determine the extent of glucose-dependent insulin release. This review discusses recent advances in our understanding of inter-organ communications that regulate beta cell insulin release in response to elevated glucose levels.

Spatial and temporal coordination of insulin granule exocytosis in intact human pancreatic islets.

Insulin secretion is widely studied because it plays a central role in glucose homeostasis and diabetes. Processes from insulin granule fusion in beta cells to in vivo insulin secretion have been elucidated, but data at the cellular level do not fully account for several aspects of the macroscopic secretory pattern. Here we investigated how individual secretory events are coordinated spatially and temporally within intact human islets. We used the fluorescent probe neuropeptide Y (NPY)-pHluorin to visualise insulin granule secretion in isolated intact human islets. We found that individual beta cells respond to increases in glucose concentration by releasing insulin granules in very discrete bursts with periods consistent with in vivo pulsatile insulin secretion. In successive secretory bursts during prolonged exposure to high glucose levels, secretory events progressively localised to preferential release sites, coinciding with the transition to second phase insulin secretion. Granule secretion was very synchronised in neighbouring beta cells, forming discrete regional clusters of activity. These results reveal how individual secretory events are coordinated to produce pulsatile insulin secretion from human islets.

Mast cells infiltrate pancreatic islets in human type 1 diabetes.

Beta cell destruction in human type 1 diabetes occurs through the interplay of genetic and environmental factors, and is mediated by immune cell infiltration of pancreatic islets. In this study, we explored the role of mast cells as an additional agent in the pathogenesis of type 1 diabetes insulitis. Pancreatic tissue from donors without diabetes and with type 1 and 2 diabetes was studied using different microscopy techniques to identify islet-infiltrating cells. The direct effects of histamine exposure on isolated human islets and INS-1E cells were assessed using cell-survival studies and molecular mechanisms. A larger number of mast cells were found to infiltrate pancreatic islets in samples from donors with type 1 diabetes, compared with those from donors without diabetes or with type 2 diabetes. Evidence of mast cell degranulation was observed, and the extent of the infiltration correlated with beta cell damage. Histamine, an amine that is found at high levels in mast cells, directly contributed to beta cell death in isolated human islets and INS-1E cells via a caspase-independent pathway. These findings suggest that mast cells might be responsible, at least in part, for immune-mediated beta cell alterations in human type 1 diabetes. If this is the case, inhibition of mast cell activation and degranulation might act to protect beta cells in individuals with type 1 diabetes.

Progressive glucose stimulation of islet beta cells reveals a transition from segregated to integrated modular functional connectivity patterns.

Collective beta cell activity in islets of Langerhans is critical for the supply of insulin within an organism. Even though individual beta cells are intrinsically heterogeneous, the presence of intercellular coupling mechanisms ensures coordinated activity and a well-regulated exocytosis of insulin. In order to get a detailed insight into the functional organization of the syncytium, we applied advanced analytical tools from the realm of complex network theory to uncover the functional connectivity pattern among cells composing the intact islet. The procedure is based on the determination of correlations between long temporal traces obtained from confocal functional multicellular calcium imaging of beta cells stimulated in a stepwise manner with a range of physiological glucose concentrations. Our results revealed that the extracted connectivity networks are sparse for low glucose concentrations, whereas for higher stimulatory levels they become more densely connected. Most importantly, for all ranges of glucose concentration beta cells within the islets form locally clustered functional sub-compartments, thereby indicating that their collective activity profiles exhibit a modular nature. Moreover, we show that the observed non-linear functional relationship between different network metrics and glucose concentration represents a well-balanced setup that parallels physiological insulin release.

Contribution of Different Mechanisms to Pancreatic Beta-cell Hyper-secretion in Non-obese Diabetic (NOD) Mice during Pre-diabetes

The development of insulin-dependent diabetes mellitus (IDDM) results from the selective destruction of pancreatic beta-cells. Both humans and spontaneous models of IDDM, such as NOD mice, have an extended pre-diabetic stage. Dynamic changes in beta-cell mass and function during pre-diabetes, such as insulin hyper-secretion, remain largely unknown. In this paper, we evaluated pre-diabetic female NOD mice at different ages (6, 10, and 14 weeks old) to illustrate alterations in beta-cell mass and function as disease progressed. We found an increase in beta-cell mass in 6-week-old NOD mice that may account for improved glucose tolerance in these mice. As NOD mice aged, beta-cell mass progressively reduced with increasing insulitis. In parallel, secretory ability of individual beta-cells was enhanced due to an increase in the size of slowly releasable pool (SRP) of vesicles. Moreover, expression of both SERCA2 and SERCA3 genes were progressively down-regulated, which facilitated depolarization-evoked secretion by prolonging Ca(2+) elevation upon glucose stimulation. In summary, we propose that different mechanisms contribute to the insulin hyper-secretion at different ages of pre-diabetic NOD mice, which may provide some new ideas concerning the progression and management of type I diabetes.